I. Field of the Invention
The present invention relates to a protection arrangement for a switching transistor inverter circuit, and, more particularly, to an emergency lighting circuit including an inverter with control means for operating a gaseous discharge lamp from a DC electrical energy source upon failure of the primary AC source, the circuit being provided with means for protecting the control means from capacitive displacement currents flowing as a reslt of rapid excursions in potential with respect to ground in the system.
II. Description of the Prior Art
Electric power failures due to inclement weather conditions and equipment breakdowns have been a plague for many years. A power failure, no matter what the cause may be, may very well jeopardize human life due to lighting system failure. There are, therefore, many installations which require some type of emergency lighting system which will automatically come into operation upon the occurrence of a power failure. result high efficiency of a fluorescent lamp makes it especially valuable for use in such an emergency lighting system.
Presently available emergency lighting systems are generally of the type using a transistor switching inverter and wherein a single lamp or group of lamps is used for both normal AC operation of the lighting system and for the emergency system, a battery being used as the power source for energizing the transistor inverter and the lamps when the AC line voltage fails. Advantageously, in order to control the operation of such a system, means are provided which may take the form of monolithic integrated circuit (IC). A system using such an IC controller is disclosed and claimed in U.S. Pat. No. 3,921,005 -- Watrous, assigned to the assignee of the present invention. Such a controller performs a variety of functions as disclosed therein. However, rapid excursions in potential in the system with respect to ground may cause capacitive displacement currents to flow in the controller thereby possibly producing shifts in the circuit operating points, if the circuit continues to operate at all.
It is desirable, therefore, to provide an emergency lighting system including an inverter circuit wherein such capacitive coupling effects are minimized.
Accordingly, it is an object of the present invention to provide an emergency lighting system having an inverter with control means wherein means are provided for minimizing the effects of and for protecting the system control means from capacitive displacement currents flowing in the system.